Thesis presented December 13, 2021
Abstract: Single-photons based qubits are promising for applications such as in quantum computing, quantum metrology, and quantum communication where they can be used as flying-qubits. However, challenges faced in single-photon-based technologies are efficient light extraction, scalability and high temperature operability. CdSe quantum dots (QD) have shown promise for single-photon emission up to room temperatures in the visible range (∼550 nm), useful for free-space communication. To tackle light extraction and scalability issues, we propose a system where a CdSe QD is embedded in a ZnSe tapered nanowire (NW), realized with Molecular beam epitaxy (MBE). A tapered NW shape is targeted to efficiently extract light from the QD-NW in free-space. Moreover, this QD-NW system is a single unit that can be picked up and transferred from one substrate to another. In this thesis, first, finite-element-method numerical simulations were performed to optimize the shape and size of our QD-NWs for efficient light collection along the NW axis. Then this optimized QD-NW shape is realized with MBE. The MBE growth conditions are studied and optimized to control the radial and axial growth of the NWs, grown under gold-nanoparticle catalysed vapor-solid-solid growth mechanism. Growth of reproducible and vertically oriented CdSe-ZnSe QD-NWs (QD diameter ~6 nm, height ~4 nm) with a tapered Zn(Mg)Se shell is achieved. Then, the emission properties of these QD-NWs are studied from cryogenic to room temperatures with continuous and pulse excitation. It is shown that even when single-photon emission is confirmed with anti-bunching measurements under continuous excitation, it does not confirm if the emitter will emit single-photons on-demand. For QD-NWs where MBE growth parameters were optimized, single-photon emission is achieved up to room temperatures. Finally, prospects for evanescent coupling of QD-NW to silicon nitride waveguides for integrated photonics applications are discussed.
Keywords: Single Photon source, II-VI semiconductor, nanowire growth
On-line thesis.